Powder coating compositions containing functional polysiloxanes

ABSTRACT

Improved powder coating compositions containing novel polysiloxanes having various reactive functional groups are disclosed. The compositions are particularly useful as thermosetting powder coating compositions where they provide excellent filiform corrosion resistance.

This is a Divisional Application of patent application Ser. No.08/995,790, now U.S. Pat. No. 6,046,276 filed Dec. 22, 1997, which is aContinuation-in-Part Application of patent application Ser. No.08/904,597, filed on Aug. 1, 1997, now U.S. Pat. No. 5,939,491, issuedAug. 17, 1999.

BACKGROUND OF THE INVENTION

The present invention relates to an improved powder coating compositioncomprising a solid particulate film-forming mixture of a polymercontaining reactive functional groups and a curing agent havingfunctional groups reactive with the functional groups of the polymer,which components are well known in the art, wherein the improvementcomprises an organic polysiloxane having various reactive functionalgroups reactive with the functional groups of the polymer and/or thecuring agent. More particularly, this invention relates to improvedpowder coating compositions which provide enhanced filiform corrosionresistance.

Powder coating compositions for use in painting are extremely desirable.Such coating compositions greatly reduce and can even eliminate theorganic solvents used in liquid paints. When the powder coatingcomposition is thermally cured, little, if any, volatile material isgiven off to the surrounding environment. This is a significantadvantage over liquid paints in which organic solvent is volatilizedinto the surrounding atmosphere when the paint is cured by heating.

A particular problem which often results from the use of powdercoatings, particularly over aluminum substrates, is filiform corrosionwhich is a type of localized corrosion that affects painted metals(usually steel, aluminum and magnesium). Filiform corrosion generallyoccurs in wet environments at the site of a surface defect in thepresence of soluble ionic species. As described in Filiform Corrosion inPolymer-coated Metals, A. Bautista, PROGRESS IN ORGANIC COATINGS 28 atpages 49-58 (1996), this deterioration process gives rise to corrosionproducts which are characterized by a filamentous, wormlike appearanceunder the coatings. The “filaments” typically exhibit an arborescentstructure and grow directionally under the coating.

As filiform corrosion results in delamination of an organic coating froma metal substrate, thereby exposing the metal to the environment, it hasbecome a matter for increasing concern in the areas of automotive,industrial and architectural coatings. Accordingly, it is desirable toprovide a powder coating composition with improved filiform corrosion.It has been found that incorporation of certain organic polysiloxaneshaving functional groups reactive with the functional groups of thepolymer and/or the curing agent improves the filiform corrosionresistance of the powder coating composition.

Polysiloxanes with hydroxyl functional groups (i.e., polysiloxanepolyols) are well known in the art. Japanese Patent Publication 48-19941describes polysiloxane polyols which are obtained by the dehydrogenationreaction between a polysiloxane hydride and an aliphatic polyhydricalcohol or polyoxyalkylene alcohol to introduce the alcoholic hydroxygroups onto the polysiloxane backbone. In practice, however, it isdifficult to obtain an industrially significant yield of suchpolysiloxane polyols because such a hydrosilylation reaction readilygels. Another problem encountered with this hydrosilylation reaction isthe difficulty in obtaining a solvent capable of dissolving bothreactants. Strongly hydrophilic alcohols such as polyglycerols arehighly soluble in alcohols and water, but insoluble in hydrocarbonsolvents. Polysiloxanes, however, are generally only soluble inhydrocarbon solvents such as toluene or n-hexane.

U.S. Pat. No. 4,431,789 to Okazaki et al. discloses a polysiloxanepolyol which is obtained by the hydrosilylation reaction between apolysiloxane containing silicon hydride and a polyglycerol compoundhaving an aliphatically unsaturated linkage in the molecule. Examples ofsuch polyglycerol compounds are those obtained by the reaction of allylalcohol and glycidol or by the reaction of diglycerin and allyl glycidylether. This reaction, a so-called hydrosilylation reaction, is theaddition reaction between an organosilicon compound having a hydrogenatom directly bonded to the silicon atom, i.e., a polysiloxane hydride,and an organic compound having aliphatic unsaturation in the moleculecarried out in the presence of a catalytic amount of a Group VIII noblemetal. The hydrosilylation reaction can proceed readily in the presenceof an alcoholic solvent which can dissolve both reactants. The resultingpolysiloxane polyols are useful in coatings as non-ionic surface activeagents.

U.S. Pat. No. 5,260,469 discloses butoxylated polysiloxane polyols whichare disclosed as being useful in cosmetics. U.S. Pat. No. 5,248,789discloses epoxy functional polysiloxanes which are formed by reacting apolysiloxane-containing silicon hydride with allyl glycidyl ether.

U.S. patent application Ser. No. 08/904,598 now U.S. Pat. No. 5,916,992discloses polysiloxane polyols obtained by the hydrosilylation of apolysiloxane containing silicon hydride with an alkenyl polyoxyalkylenealcohol. These polysiloxane polyols can contain two or more primaryhydroxyl terminal functional groups per pendant group.

U.S. patent application Ser. No. 08/904,597 now U.S. Pat. No. 5,939,491discloses acetoacetate functional polysiloxanes and coating compositionscontaining such. The acetoacetate functional polysiloxanes are obtainedby the transesterification of a polysiloxane polyol with anacetoacetate. The coating composition taught by this reference comprisesan acetoacetate functional polysiloxane, a polyamine or blockedpolyamine, and, optionally a polyacrylate curing agent. This coatingcomposition is liquid in form and typically prepared as a two-pack,ambient-cured system.

Pending U.S. Patent Application Ser. No. 08/904,597 discloses curablecompositions comprising an organic polysiloxane containing variousreactive functional groups and a curing agent containing functionalgroups which are reactive with the functional groups of polysiloxane.The organic polysiloxanes of this reference contain reactive functionalgroups such as OH, COOH, NCO, carboxylate, primary and secondary amine,amide, carbamate and epoxy functional groups.

These polysiloxanes are obtained by further reacting the hydroxyl groupsof the polysiloxane polyols with other groups to provide variousreactive functional groups pendant from the polysiloxane backbone. Suchreactive functional groups allow incorporation of the polysiloxanemoiety into curable compositions which can contain a variety of reactivecomponents, including a variety of curing agents.

SUMMARY OF THE INVENTION

The powder coating composition of the invention comprises a solidparticulate film-forming mixture of (a) a polymer containing reactivefunctional groups and (b) a curing agent having functional groupsreactive with the functional groups of the polymer, such mixture as iswell known in the art, wherein the improvement comprises (c) an organicpolysiloxane having reactive functional groups which are reactive withthe functional groups of (a) and/or (b), said polysiloxane having thefollowing general structural formula:

where m is at least 1; m′ is 0 to 50; n is 0 to 50; the R groups aremonovalent hydrocarbon group connected to the silicon atoms; R^(a) hasthe following structure:

R₁—O—X  (III)

wherein R₁ is alkylene, oxyalkylene or alkylene aryl; and X is a moietycontaining a functional group selected from the group consisting of OH,COOH, NCO, carboxylate such as ester, carbonate and anhydride, primaryamine, secondary amine, amide, thiol, carbamate, and epoxy functionalgroups.

DETAILED DESCRIPTION OF THE INVENTION

In the structural formulas of (I) and (II), the various R groups can bethe same or different, and it is usually the case that the R groups willbe mixed monovalent hydrocarbon groups.

By monovalent hydrocarbon groups is meant organic groups containingessentially carbon and hydrogen. The hydrocarbon groups may bealiphatic, aromatic, cyclic or acyclic and may contain from 1 to 24 (inthe case of aromatic from 3 to 24) carbon atoms. Optionally, thehydrocarbon groups may be substituted with heteroatoms, typicallyoxygen. Examples of such monovalent hydrocarbon groups are alkyl,alkoxy, aryl, alkaryl or alkoxyaryl groups.

By alkylene is meant acyclic or cyclic alkylene groups having a carbonchain length of from C₂ to C₂₅. Examples of suitable alkylene groups arethose derived from propene, butene, pentene, 1-decene, isoprene, myrceneand 1-heneicosene. By oxyalkylene is meant an alkylene group containingat least one ether oxygen atom and having a carbon chain length of fromC₂ to C₂₅, preferably of from C₂ to C₄. Examples of suitable oxyalkylenegroups are those associated with trimethylolpropane monoallylether,pentaerythritol monoallylether, trimethylolpropane diallylether,polyethoxylated allyl alcohol and polypropoxylated allyl alcohol. Byalkylene aryl is meant an acyclic alkylene group containing at least onearyl group, preferably phenyl, and having an alkylene carbon chainlength of from C₂ to C₂₅. The aryl group may optionally be substituted.Suitable substituent groups may include hydroxyl, benzyl, carboxylicacid and aliphatic groups. Examples of suitable alkylene aryl groupsinclude styrene and 3-isopropenyl-α,α-dimethylbenzyl isocyanate.

Formulae (I) and (II) are diagrammatic, and it is not intended to implythat the parenthetical portions are necessarily blocks, although blocksmay be used where desired. In many cases the compound is more or lessrandom, especially when more than a few siloxane units are employed andwhen mixtures are used. In those instances where more than a fewsiloxane units are used and it is desired to form blocks, oligomers arefirst formed and then these are joined to form the block compound. Byjudicious choice of reactants, compounds having an alternating structureor blocks of alternating structure may be used.

As mentioned above, the powder coating composition is preferably athermosetting composition comprising:

(a) at least one film-forming polymer which contains reactive functionalgroups;

(b) a curing agent containing functional groups which are reactive withthe functional groups of said polymer; and

(c) an organic polysiloxane which contains functional groups which arereactive with the functional groups of (a) and/or (b), said polysiloxanehaving the general structural formula (I) or (II), where m, m′, n, R,R₁, R^(a) and X are as described above. Preferably, n+m and n+m′ is 2 or3.

The reactive functional groups of (a) and (c) can be the same ordifferent, but preferably both are reactive with the functional groupsof the curing agent (b). Examples of such reactive functional groups of(a) and/or (c) include OH, COOH, NCO, carboxylate, such as ester,carbonate and anhydride groups, primary amine, secondary amine, amide,thiol, carbamate and epoxy functional groups.

Polysiloxanes Containing Reactive Functional Groups

In a preferred embodiment of the invention, X is a moiety which containsCOOH functional groups. More preferably, when X is a group containingCOOH functional groups, the organic polysiloxane is the reaction productof the following reactants:

(a) a polysiloxane polyol having the following structure:

 where m is at least 1; m′ is 0 to 50; n is 0 to 50; the R groups aremonovalent hydrocarbon groups connected to the silicon atoms; R^(b) hasthe following structure:

R₁—O—Y  (VII)

wherein R₁ is alkylene, oxyalkylene or alkylene aryl; and Y is H,mono-hydroxy substituted alkylene or oxyalkylene, or has the followinggeneral structural formula:

R₂—(—CH₂—OH)_(p) wherein p is 2 or 3; and  (IV)

where R₂ is CH₂—C—R₃ when p is 2 and R₃ is C₁ to C₄ alkyl, or

(b) at least one polycarboxylic acid or anhydride, preferably ananhydride.

Examples of anhydrides, suitable for use in the present invention asreactant (b) immediately above include hexahydrophthalic anhydride,methyl hexahydrophthalic anhydride, phthalic anhydride, trimelliticanhydride, succinic anhydride, chlorendic anhydride, alkenyl succinicanhydride and substituted alkenyl anhydrides such as octenyl succinicanhydride and mixtures thereof.

In another embodiment of the invention, X is a moiety which containsepoxy functional groups. Preferably, when X is a group containing epoxyfunctional groups, the organic polysiloxane is the reaction product ofthe following reactants:

(a) a polysiloxane polyol having the structure of formula (V) or (VI),where m, m′, n, R, R^(b) and Y are as described above for thesestructures; and

(b) at least one polyepoxide, preferably an aliphatic or cycloaliphaticpolyepoxide, or mixtures thereof.

Examples of polyepoxides suitable for use in the present invention asreactant (b) immediately above are those well known in the art, such asthose described in U.S. Pat. No. 4,681,811 at col. 4, line 52 to col. 5,line 50, hereby incorporated by reference.

In yet another embodiment of the invention, X is an oligomeric orpolymeric urethane or urea-containing material which is terminated withNCO, OH, primary amine or secondary amine functional groups. When X issuch a moiety, the organic polysiloxane is the reaction product of thefollowing reactants:

(a) a polysiloxane polyol having the structure of formula (V) or (VI),where m, m′, n, R, R^(b) and Y are as described above for thesestructures;

(b) at least one polyisocyanate; and

(c) optionally at least one compound having at least 2 active H atomsper molecule selected from the group consisting of hydroxyl, primaryamine and secondary amine.

Examples of polyisocyanates suitable for use in the present invention asreactant (b) immediately above are commonly known in the art, such asthose described in U.S. Pat. No. 4,046,729 at col. 5, line 26 to col. 6,line 28, hereby incorporated by reference. Preferred are aliphatic orcycloaliphatic diisocyanates, or mixtures thereof.

Examples of compounds having at least 2 active H atoms per molecule, arepolyols and polyamines containing primary and/or secondary amines.Examples of polyols suitable for use in the present invention asreactant (c) immediately above are well known in the art, such as thosedescribed in U.S. Pat. No. 4,046,729 at col. 7, line 52 to col. 10, line35, hereby incorporated by reference. Examples of polyamines suitablefor use in the present invention as reactant (c) immediately above arewell known in the art, such as those described in U.S. Pat. No.4,046,729 at col. 6, line 61 to col. 7, line 32, and in U.S. Pat. No.3,799,854 at col. 3, lines 13 to 50, both hereby incorporated byreference.

Reaction conditions and the ratio of the reactants (a), (b) and (c) areselected so as to form the desired terminal group.

In another embodiment of the invention, X is an oligomeric or polymericester-containing moiety which is terminated with OH or COOH functionalgroups. When X is such a group, the organic polysiloxane is thecondensation reaction product of the following reactants:

(a) a polysiloxane polyol having the structure of formula (V) or (VI),where m, m′, n, R, R^(b) and Y are as described above for thesestructures;

(b) at least one COOH group containing material; and

(c) at least one organic polyol.

Examples of COOH containing groups suitable for use in the presentinvention as reactant (b) immediately above are carboxylic acid groupcontaining polymers well known in the art, such as those described inU.S. Pat. No. 4,681,811 at col. 6, line 38; col. 7, line 33; col. 7,line 47; and col. 8, line 2, hereby incorporated by reference. Preferredare aliphatic and cycloaliphatic polycarboxylic acids and mixturesthereof.

Examples of organic polyols suitable for use in the present invention asreactant (c) immediately above are polymeric polyols well known in theart, such as those described in U.S. Pat. No. 4,798,746 at col. 3, line20 to col. 5, line 61, hereby incorporated by reference.

In still another embodiment of the invention, X is a moiety whichcontains carbamate functional groups. Preferably, when X is such amoiety, the organic polysiloxane is the reaction product of thefollowing reactants:

(a) a polysiloxane polyol having the structure of formula (V) or (VI),where m, m′, n, R, R^(b) and Y are as described above for thesestructures; and

(b) at least one compound selected from the group consisting of alkylcarbamate, isocyanic acid, urea, and mixtures thereof, preferably alkylcarbamate.

Reaction conditions and the ratio of the reactants (a), (b) and (c) areselected so as to form the desired terminal group. The various materialsused to form the functional group containing polysiloxanes of thepresent invention are selected such that the resultant material has ahigh glass transition temperature (T_(g)), i.e., greater than 30° C. TheT_(g) of the polymer can be calculated as described by Fox in Bull.Amer. Physics. Soc., 1, 3 page 123 (1956). The T_(g) can also bemeasured experimentally and differential scanning calorimetry can beused (rate of heating 10° C. per minute, T_(g) taken at the firstinflection point). Unless otherwise indicated, the stated T_(g) as usedherein refers to the calculated T_(g).

Polymers Containing Functional Groups

The powder coating compositions of the present invention comprisepolymers containing functional groups such as hydroxyl, carboxylic acid,carbamate, amide and carboxylate functional groups.

The use in powder coatings of acrylic, polyester, polyether andpolyurethane oligomers and polymers having hydroxyl functionality iswell known in the art. Monomers for the synthesis of such oligomers andpolymers are chosen such that the resulting oligomers and polymers havea T_(g) greater than 50° C. Examples of such oligomers and polymershaving hydroxyl functional groups suitable for use in the powder coatingcompositions of the present invention are those described in U.S. Pat.No. 5,646,228 at column 5, line 1 to column 8, line 7, incorporated byreference herein.

The use in powder coatings of acrylic polymers having carboxylic acidfunctionality is well known in the art. Monomers for the synthesis ofthe acrylic polymers having carboxylic acid functionality suitable foruse in the powder coating compositions of the present invention arechosen such that the resulting acrylic polymer has a T_(g) greater than40° C. Examples of carboxylic acid group containing acrylic polymers arethose described in U.S. Pat. No. 5,214,101 at col. 2, line 59 to col. 3,line 23, hereby incorporated by reference.

The use in powder coatings of polyester polymers having carboxylic acidfunctionality is well known in the art. Monomers for the synthesis ofthe polyester polymers having carboxylic acid functionality suitable foruse in the powder coating compositions of the present invention arechosen such that the resulting polyester polymer has a T_(g) greaterthan 50° C. Examples of carboxylic acid group containing polyesterpolymers are those described in U.S. Pat. No. 4,801,680 at col. 5, lines38 to 65, hereby incorporated by reference.

Besides carboxylic acid group-containing acrylic polymers, the powdercoating compositions of the present invention can, and typically do,contain a second carboxylic acid group-containing material selected fromthe class of C₄ to C₂₀ aliphatic dicarboxylic acids, polymericpolyanhydrides, low molecular weight polyesters having an acidequivalent weight from about 150 to about 750 and mixtures thereof. Thismaterial is crystalline and is preferably a low molecular weightcrystalline carboxylic acid group-containing polyester.

Also useful in powder coating compositions are acrylic, polyester andpolyurethane polymers containing carbamate functional groups, such asthose well known in the art. Examples of such polymers having carbamatefunctionality suitable for use in the powder coating compositions of theinvention are described in WO Pat. No. 94/10213. Monomers for thesynthesis of such polymers for use in the powder coating compositionsare chosen such that the resulting polymer has a high T_(g), that is, aT_(g) greater than 40° C.

Curing Agents

In one preferred embodiment of the invention, the curing agent is ablocked polyisocyanate. Blocked isocyanates as curing agents for OH andprimary and/or secondary amino group containing materials are well knownin the art. Examples of blocked isocyanates suitable for use as curingagents in the powder coating compositions of the present invention arethose described in U.S. Pat. No. 4,988,793, col. 3, lines 1 to 36,hereby incorporated by reference.

Polyepoxides as curing agents for COOH functional group containingmaterials are well known in the art. Examples of polyepoxides suitablefor use as curing agents in the powder coating compositions of thepresent invention are those described in U.S. Pat. No. 4,681,811 at col.5, lines 33 to 58, hereby incorporated by reference.

Polyacids as curing agents for epoxy functional group containingmaterials are well known in the art. Examples of polyacids suitable foruse as curing agents in the electrodepositable coating compositions ofthe present invention are those described in U.S. Pat. No. 4,681,811 atcol. 6, line 45 to col. 9, line 54, hereby incorporated by reference.

Polyols, that is, material having an average of two or more hydroxylgroups per molecule, can be used as curing agents for NCO functionalgroup containing materials and anhydrides, and are well known in theart. Polyols for use in the powder coating compositions of the presentinvention are selected such that the resultant material has a high glasstransition temperature, i.e., greater than 50° C.

Anhydrides as curing agents for epoxy functional group containingmaterials are well known in the art. Examples of such curing agentsinclude trimellitic anhydride, benzophenone tetracarboxylic dianhydride,pyromellitic dianhydride, tetrahydrophthalic anhydride, and the like asdescribed in U.S. Pat. No. 5,472,649 at col. 4, lines 49 to 52.

Aminoplasts as curing agents for OH, COOH and carbamate functional groupcontaining materials are well known in the art. Examples of such curingagents suitable for use in the present invention are aldehydecondensates of glycoluril, which give high melting crystalline productsuseful in powder coatings. While the aldehyde used is typicallyformaldehyde, other aldehydes such as acetaldehyde, crotonaldehyde, andbenzaldehyde can be used.

The organic polysiloxane which contains reactive functional groups ispresent in the powder coating composition in an amount of about 1 toabout 15, preferably from about 3 to about 7 percent by weight based ontotal weight of the powder coating composition. The polymer containingfunctional groups is present in amounts of about 60 to about 90 percentby weight, preferably from about 70 to about 85 percent by weight basedon total weight of the powder coating composition. The curing agent ispresent in amounts of about 5 to 15, preferably about 6 to 10 percent byweight based on total weight of the powder coating composition.

In the preferred embodiment of the invention, the powder coatingcomposition additionally contains a polyester adduct of pentaerythritoland dodecanedioic acid (1:4). The polyester adduct is typically presentin the powder coating composition of the invention in an amount of fromabout 1 to about 20 percent, preferably from about 5 to about 15 percentand more preferably from about 4 to about 6 percent by weight based ontotal weight of the powder coating composition.

The powder coating compositions of the present invention can optionallyinclude other materials such as pigments, fillers, light stabilizers,anti-oxidants and flow control agents and anti-popping agents.

A pigment can be included in the coating in amounts of up to 60 per centby weight based on total weight of the composition in order to give asuitable color to the resultant coating. Suitable pigments include, forexample, titanium dioxide, ultramarine blue, phthalocyanine blue,phthalocyanine green, carbon black, graphite fibrils, black iron oxide,chromium green oxide, ferride yellow and quindo red.

In addition, the powder coating composition may include fumed silica orthe like to reduce caking of the powder during storage. An example of afamed silica is commercially available from Cabot Corporation under thetrademark CAB-O-SIL. The fumed silica is present in amounts ranging upto 1 percent by weight based on total weight of the powder coatingformulations.

For good exterior durability, the compositions also can containultraviolet light absorbing agents, ultraviolet light stabilizers andantioxidants. Such materials are commercially available from Ciba-Geigyunder the trademarks TINUVIN and IRGANOX. The ultraviolet lightabsorbing agents, ultraviolet light stabilizers and antioxidants, whenused, are typically present in the compositions individually in amountsup to 6 percent by weight based on weight of resin solids.

One group of suitable flow control agents are acrylic polymers such aspolylauryl acrylate, polybutyl acrylate, poly(2-ethylhexyl) acrylate,poly(ethyl-2-ethylhexyl) acrylate, polylauryl methacrylate andpolyisodecenyl methacrylate. The flow control agent may also be afluorinated polymer such as an ester of polyethylene glycol orpolypropylene glycol and fluorinated fatty acids, for example, an esterof polyethylene glycol of a molecular weight of over 2,500 andperfluorooctanoic acid. Polymeric siloxanes of molecular weights over1,000 may also be used as a flow control agent, for example,poly(dimethylsiloxane) or poly(methylphenyl)siloxane. The flow controlagent, when used, is present in amounts up to 5 percent by weight basedon total weight of the coating composition.

Anti-popping agents can be added to the composition to allow anyvolatile material to escape from the film during baking. Benzoin is apreferred anti-popping agent and when used is generally present inamounts up to 3.0 percent by weight based on total weight of the powdercoating composition.

The powder coating compositions are typically prepared by melt blendingthe ingredients. This can be accomplished by first blending theingredients in a high shear mixer such as a planetary mixer, an thenmelt blending in an extruder from about 80° C. to about 13° C. Theextrudate is then cooled and pulverized into a particulate material canbe applied by spraying.

The particulate powder coating compositions can be applied directly to asubstrate of, for example, metal such as steel or aluminum, or to aprimed metal substrate. In particular, when the particulate coatingcompositions of the invention are applied to aluminum substrates, animprovement in filiform corrosion resistance is noted. Application canbe by spraying, and in the case of a metal substrate, by electrostaticspraying which is preferred, or by the use of a fluidized bed. Thecoating composition can be applied as a primer or as a primer surfacer,or as a topcoat or as a finishing coat. The powder coating can beapplied in a single sweep or in several passes to provide a film havinga thickness after cure of from about 1 to 10 mils, usually about 2.0 to4.0 mils.

After application of the powder coating composition, the powder coatedsubstrate is baked at a temperature sufficient to cure the product,typically at about 250° F. to about 400° F. (121° to 204° C.) for about1 to 60 minutes, and preferably at about 300° F. to about 350° F. (160°to 175° C.) for about 15 to 30 minutes.

The following examples illustrate the invention and should not beconstrued as a limitation on the scope thereof. Unless specificallyindicated otherwise, all percentages and amounts are by weight.

EXAMPLES

Example 1 describes the preparation of a polysiloxane tetrol via thehydrosilylation reaction of MASIL WAX™, a polysiloxane containingsilicon hydride, and trimethylol propane monoallylether. Example 2describes the synthesis of an acid functional group containingpolysiloxane which is reaction product of the polysiloxane tetrol ofExample 1 and hexahydrophthalic anhydride. Example 3 describes thepreparation of a polysiloxane tetrol via the hydrosilylation reaction ofMASIL WAX™, a polysiloxane containing silicon hydride, and4-vinyl-1,2-cyclohexanediol. Example 4 describes the preparation of anacid functional group containing polysiloxane which is reaction productof the polysiloxane tetrol of Example 3 and hexahydrophthalic anhydride.

Example A describes the preparation of three powder coatingcompositions. Examples A-1 and A-2 represent two powder coatingcompositions which contain varying levels of the acid functional groupcontaining polysiloxane of Example 2, while Comparative Example A-3represents a powder coating composition which contains no acidfunctional polysiloxane. The following Table 1 illustrates theadvantages in filiform corrosion resistance exhibited by thecompositions of A-1 and A-2 which contain the acid functional groupcontaining polysiloxane.

Example B describes the preparation of three powder coatingcompositions. Examples B-1 and B-2 represent two powder coatingcompositions which contain varying levels of the acid functional groupcontaining polysiloxane of Example 4, while Comparative Example B-3represents a powder coating composition which contains no acidfunctional polysiloxane. The following Table 2 illustrates theadvantages in filiform corrosion resistance exhibited by thecompositions of B-1 and B-2 which contain the acid functional groupcontaining polysiloxane.

FUNCTIONAL GROUP CONTAINING POLYSILOXANES Example 1

This example describes the preparation of polysiloxane tetrol, a productof the hydrosilylation of MASILWAX™ polysiloxane with an approximatedegree of polymerization of 3 to 4, i.e., (Si—O)₃ to (Si—O)₄. Thepolysiloxane tetrol was prepared from the following mixture ofingredients:

Equivalent Parts By Weight Ingredients Weight Equivalents (grams) ChargeI: Trimethylolpropane 174.0 9.4 1630.0 monoallylether Charge II: MASILWAX¹ 156.7² 9.4 1467.4 Charge III: Chloroplatinic acid 10 ppm¹Polysiloxane-containing silicon hydride, obtained from PPG Industries,Inc. ²Equivalent weight based on mercuric bichloride determination.

To a suitable reaction vessel equipped with a means for maintaining anitrogen blanket, Charge I and an amount of sodium bicarbonateequivalent to 20 to 25 ppm of total monomer solids were added at ambientconditions and the temperature was gradually increased to 75° C. under anitrogen blanket. At that temperature, about 5.0% of Charge II was addedunder agitation, followed by the addition of Charge III, equivalent to10 ppm of active platinum based on total monomer solids. The reactionwas then allowed to exotherm to 95° C. at which time the remainder ofCharge II was added at a rate such that the temperature did not exceed95° C. After completion of this addition, the reaction temperature wasmaintained at 95° C. and monitored by infrared spectroscopy fordisappearance of the silicon hydride absorption band (Si—H, 2150 cm⁻¹).

Example 2

This example describes the preparation of a polysiloxane containing COOHfunctional groups, a product of the polysiloxane polyol of Example 1,and a polycarboxylic anhydride. The polysiloxane having COOH functionalgroups was prepared from the following mixture of ingredients:

Equivalent Parts By Weight Ingredients Weight Equivalents (grams) ChargeI: Polysiloxane polyol of 183.9 14.51 2670.0 Example 1 Charge II:Hexahydrophthalic 154.0 14.51 2235.9 anhydride

To a suitable reaction vessel, equipped with a means for maintaining anitrogen blanket, Charge I was added at ambient temperature and heatedto 125° C. under a nitrogen blanket. Charge II was added dropwise, undermild agitation. Temperature was held at 125° C. to a stalled acid value(as measured by the depletion of anhydride), and the disappearance ofanhydride as followed by IR spectroscopy.

Example 3

This example describes the preparation of polysiloxane tetrol, a productof the hydrosilylation of MASIL WAX™ polysiloxane with an approximatedegree of polymerization of 3 to 4, i.e., (Si—O)₃ to (Si—O)₄. Thepolysiloxane tetrol was prepared from the following mixture ofingredients:

Equivalent Parts By Weight Ingredients Weight Equivalents (grams) ChargeI: 4-Vinyl-1,2- 142.0 3.1 438.0 cyclohexanediol¹ Charge II: MASIL WAX153.8² 2.94 451.2 Charge III: Chloroplatinic acid 10 ppm ¹CAS No.31646-64-7.

To a suitable reaction vessel equipped with a means for maintaining anitrogen blanket, Charge I and an amount of sodium acetate equivalent toabout 20 to 25 ppm of total monomer solids was added at ambientconditions and the temperature was gradually increased to 75° C. under anitrogen blanket. At that temperature, about 5.0% of Charge II was addedunder agitation, followed by the addition of Charge III, equivalent to10 ppm of active platinum based on total monomer solids. The reactionwas then allowed to exotherm to 95° C. at which time the remainder ofCharge II was added at a rate such that the temperature did not exceed95° C. After completion of this addition, the reaction temperature wasmaintained at 95° C. and monitored by infrared spectroscopy fordisappearance of the silicon hydride absorption band (Si—H, 2150 cm⁻¹).

Example 4

This example describes the preparation of a polysiloxane containing COOHfunctional groups, the reaction product of the polysiloxane polyol ofExample 3 and a polycarboxylic anhydride. The polysiloxane having COOHfunctional groups was prepared from the following mixture ofingredients:

Equivalent Parts By Weight Ingredients Weight Equivalents (grams) ChargeI: Polysiloxane polyol of 143.7 5.7 820.0 Example 3 Charge II:Hexahydrophthalic 154.0 2.9 439.4 anhydride

To a suitable reaction vessel, equipped with a means for maintaining anitrogen blanket, Charge I was added at ambient temperature and heatedto 125° C. under a nitrogen blanket. Charge II was added dropwise, undermild agitation. Temperature was held at 125° C. to a stalled acid value(as measured by the depletion of anhydride), and the disappearance ofanhydride as followed by IR spectroscopy.

POWDER COATING COMPOSITIONS Testing Procedures

Each of the following powder coating compositions was electrostaticallyapplied to cleaned only aluminum substrate (commercially available fromACT, Inc. as A407A1), then cured as described below. The powder coatedpanels were then tested for solvent resistance, haze rating, 20° gloss,and filiform corrosion resistance. Each powder coating formulation wastested for stability and thermal shock resistance.

Solvent resistance was tested according to ASTM D5402 using methyl ethylketone double rubs. Results are reported for appearance and mar after200 double rubs, or, alternately, as the number of double rubs completedbefore breaking through the coating to the substrate. Haze rating and20° gloss were determined using a BYK-Gardner haze-glossmeter.

Filiform corrosion resistance was tested by scribing the cured coatedsubstrate, exposing the scribed test panel in the Copper AcceleratedAcetic Acid Salt Spray (“CASS”) test cabinet according to ASTM B368-68for 6 hours, then thoroughly rinsing the panel with deionized water.These rinsed panels were subsequently exposed to an 85% relativehumidity/60° C. environment for a period of up to 4 weeks. Resultsreported represent the average length (in millimeters) of corrosionfiliments as measured outward from the scribe line.

Powder stability was tested by placing a sealed 2 ounce sample of thepowder coating composition in a water bath at 40° C. for one week. Thepowder was then examined for caking and/or fusing together of powderparticles. Thermal shock resistance was tested by soaking cured powdercoated panels in water at 100° F. for 4 hours, then immediatelytransferring the panels to a 30° C. bath to cool. Once cooled, panelswere scribed and within 30 seconds the scribed area was exposed to a 5psi steam blast. Panels were then visually examined for blushing, waterspotting and adhesion loss. Results are reported as pass/fail.

Example A

This example describes the preparation of three powder coatingcompositions based on a carboxylic acid functional acrylic polymer and apolyepoxide curing agent. Examples A-1 and A-2 contain varying levels ofthe carboxylic acid functional group containing polysiloxane of Example2, and Comparative Example A-3 contains no carboxylic acid functionalgroup containing polysiloxane.

Example A-1 Example A-2 Example A-3 Ingredients (grams) (grams) (grams)TGIC¹ 74.2 72.2 70.3 SCX-819² 362.2 377.0 391.8 Polysiloxane of Example2 25.70 12.90 0.00 URAFLOW B³ 2.8 2.8 2.8 Acid functional polyester⁴29.3 29.3 29.3 TINUVIN 900⁵ 5.2 5.2 5.2 EPON 1001F⁶ 17.2 17.2 17.2BYK-361⁷ 2.6 2.6 2.6 TROY-570⁸ 2.3 2.3 2.3 ¹Triglycidylisocyanuratecommercially available from CYTEC Corp. ²Acid functional acrylicpolymer, commercially available from S. C. Johnson Co. ³Benzoin,commercially available from Monsanto Chemical Co.⁴Pentaerithrytol/dodecanedioic acid (1:4 equivalents ratio).⁵2-(2′-hydroxy-benzotriazol-2-yl)-4,6-bis(methyl-l-phenylethyl)phenol,an ultraviolet absorber light stabilizer commercially available fromCiba-Geigy Corp. ⁶Polyglycidyl ether of Bisphenol A, having anequivalent weight of 1000, commercially available from Shell Oil andChemical Co. ⁷Polyamide flow control additive commercially availablefrom BYK Chemie USA ⁸Silicone/amide flow control aid, commerciallyavailable from Troy Chemical Corp.

The ingredients of each of the Examples A-1, A-2 and Comparative ExampleA-3 immediately above were mixed via typical powder compoundingtechniques. Each powder composition was electrostatically applied tocleaned only aluminum substrate then cured at 340° F. (171° C.) for 20minutes. The powder coated panels were then tested as described abovefor solvent resistance, haze rating, 20° gloss and filiform corrosionresistance. Each powder coating formulation was tested as describedabove for stability and thermal shock resistance.

The following Table 1 illustrates the advantages of improved filiformcorrosion resistance, while maintaining other performance properties,obtained by the incorporation of the carboxylic acid functional groupcontaining polysiloxane into the powder coating composition.

TABLE 1 Test performed: Example A-1 Example A-2 Example A-3 SolventResistance Pass, very Pass, slight mar Pass, slight mar slight mar 20°Gloss  98 113 116 Haze Rating 537 470 516 Stability 32° C./1 wk. Slightcake Pass Pass Thermal shock Pass Pass Pass Filiform Corrosion 4 wks: 2mm, 4 wks: 2 mm, 4 wks: 4 mm, very low very low medium density densitydensity

Example B

This example describes the preparation of three powder coatingcompositions based on an epoxy-fictional acrylic polymer and acarboxylic acid curing agent. Examples B-1 and B-2 contain varyinglevels of the carboxylic acid functional group containing polysiloxaneof Example 4, and Comparative Example B-3 contains no carboxylic acidfunctional group containing polysiloxane.

Example B-1 Example B-2 Example B-3 Ingredients (grams) (grams) (grams)GMA acrylic copolymer¹ 400.0 400.0 400.0 EPON 1001F 19.0 19.0 19.0URAFLOW B 3.0 3.0 3.0 TINUVIN 900 2.0 2.0 2.0 MODAFLOW II² 2.5 2.5 2.5Dodecanedioic acid 80.0 80.0 80.0 Polysiloxane of Example 4 30.0 60.0 —Acid functional polyester- 104.0 104.0 104.0 polyurethane³ ¹AlmatexA207S available from Reichold Chemicals, Inc²Ethylacrylate/2-ethylhexylacrylate copolymer available from MonsantoChemical Company. ³Hexanediol/isophorone diisocyanate/dodecanedioic acid(1.1:0.1:1.4 equivalents ratio).

The ingredients of each of the Examples B 1, B-2 and Comparative ExampleB-3 immediately above were mixed via typical powder compoundingtechniques. Each powder composition was electrostatically applied tocleaned only aluminum substrate then cured at 340° F. (171° C.) for 20minutes. The powder coated panels were then tested as described abovefor solvent resistance, 20° gloss and filiform corrosion resistance.Each powder coating formulation was tested as described above forstability and thermal shock resistance.

The following Table 2 illustrates the advantages of improved filiformcorrosion resistance, while maintaining other performance properties,obtained by the incorporation of the carboxylic acid functional groupcontaining polysiloxane into the powder coating composition.

TABLE 2 Test performed: Example B-1 Example B-2 Example B-3 Methyl ethylketone rubs 100+ 100+ 100+ 20° Gloss  75    93    72   Stability 32°C./1 wk. Pass Pass Pass Thermal shock Pass Pass Pass Filiform Corrosion5-10 mm 5-10 mm 10-20 mm

We claim:
 1. In a powder coating composition comprising a solidparticulate film-forming mixture of a polymer containing reactivefunctional groups and a curing agent having functional groups reactivewith the functional groups of the polymer wherein the improvementcomprises an organic polysiloxane having reactive functional groups,said polysiloxane having the following general formula:

where m is at least 1; m′ is 0 to 50; n is 0 to 50; the R groups aremonovalent hydrocarbon groups connected to the silicon atoms; R^(a) hasthe following structure: R₁—O—X wherein R₁ is alkylene, oxyalkylene oralkylene aryl; and X is a moiety containing at least one reactivefunctional group selected from the group consisting of OH, NCO,carboxylate, primary amine, secondary amine, amide, carbamate, thiol andepoxy functional groups.
 2. The powder coating composition of claim 1wherein n+m and n+m′ is 2 or
 3. 3. The powder coating composition ofclaim 1 wherein X is a moiety which contains epoxy functional groups,and the curing agent is a polycarboxylic acid.
 4. The powder coatingcomposition of claim 1 wherein when X is a moiety containing epoxyfunctional groups, the organic polysiloxane is the reaction product ofthe following: (a) a polysiloxane polyol of the following generalformula:

 where m is at least 1; m′ is 0 to 50; n is 0 to 50; the R groups aremonovalent hydrocarbon groups connected to the silicon atoms; R^(b) hasthe following structure: R₁—O—Y wherein R₁ is alkylene, oxyalkylene oralkylene aryl; and the moiety Y is H, monohydroxy-substituted alkyleneor oxyalkylene, or R₂—(—CH₂—OH)_(p) wherein p is 2 or 3; and where R₂ is

when p is 2 and R₃ is C₁ to C₄ alkyl, or R₂is

when p is 3; and (b) at least one polyepoxide.
 5. The powder coatingcomposition of claim 4 wherein the polyepoxide is selected from thegroup consisting of aliphatic polyepoxides, cycloaliphatic polyepoxides,and mixtures thereof.
 6. The powder coating composition of claim 1wherein X is an oligomeric or polymeric group containing terminal OH,NCO, carboxylate, primary amine, amide, carbamate or secondary aminefunctional groups.
 7. The powder coating composition of claim 6 whereinthe organic polysiloxane is the reaction product of: (a) a polysiloxanepolyol having the general structural formula:

 where m is at least 1; m′ is 0 to 50; n is 0 to 50; the R groups aremonovalent hydrocarbon groups connected to the silicon atoms; R^(b) hasthe following structure: R₁—O—Y wherein R₁ is alkylene, oxyalkylene oralkylene aryl; and Y is H, mono hydroxy-substituted alkylene oroxyalkylene, or R₂—(—CH₂—OH)_(p) wherein p is 2 or 3, and where R₂ is

when p is 2 and R₃ is C₁ to C₄ alkyl, or R₂ is

when p is 3; (b) at least one polyisocyanate; and (c) optionally atleast one compound containing at least two active hydrogen atoms permolecule selected from the group consisting of hydroxyl, primary amineand secondary amine.
 8. The powder coating composition of claim 7wherein the polyisocyanate is a diisocyanate.
 9. The powder coatingcomposition of claim 8 wherein the polyisocyanate is selected from thegroup consisting of aliphatic diisocyanates, cycloaliphaticdiisocyanates, aromatic polyisocyanates and mixtures thereof.
 10. Thepowder coating composition of claim 1 wherein X is an oligomeric orpolymeric ester-containing moiety which is terminated with OH functionalgroups.
 11. The powder coating composition of claim 10 wherein theorganic polysiloxane is the condensation reaction product of thefollowing: (a) a polysiloxane polyol having the general structuralformula:

 where m is at least 1; m′ is 0 to 50; n is 0 to 50; the R groups aremonovalent hydrocarbon groups connected to the silicon atoms; R^(b) hasthe following structure: R₁—O—Y  wherein R₁ is alkylene, oxyalkylene oralkylene aryl; and the moiety Y is H, monohydroxy-substituted alkyleneor oxyalkylene, or R₂—(—CH₂—OH)_(p) wherein p is 2 or 3; and where R₂ is

when p is 2 and R₃ is C₁ to C₄ alkyl, or R₂ is

when p is 3, and (b) at least one polycarboxylic acid; and (c) at leastone organic polyol.
 12. The powder coating composition of claim 11wherein the polycarboxylic acid is selected from the group consisting ofaliphatic and cycloaliphatic polycarboxylic acids and mixtures thereof.13. The powder coating composition of claim 11 wherein the organicpolysiloxane is present in an amount of from 2 to 20 percent by weightbased on total weight of the powder coating composition.